1. Field of the Invention
Aspects of the present invention relate to a hydrogen generator having double burners and a method of operating the same, and more particularly, to a hydrogen generator having double burners in order to reduce the time taken to begin a shift reaction in a shift reactor and a method of operating the same.
2. Description of the Related Art
A fuel cell is an electricity generating system that transforms the chemical energy of hydrogen and oxygen into electrical energy. The hydrogen is contained in a hydrocarbon group material such as methanol, ethanol, and/or natural gas. Fuel cell systems include a system that uses liquid hydrogen and a system that uses hydrogen gas.
A fuel cell that uses hydrogen gas includes a fuel cell stack and a fuel processor. The fuel cell stack constitutes a main body of the fuel cell and has a few to a few tens of unit cells in its fuel cell structure, each having a membrane electrode assembly (MEA) and a separator.
FIG. 1 is a block diagram of a conventional fuel cell system.
Referring to FIG. 1, a fuel that includes hydrogen atoms is reformed into hydrogen gas in a fuel processor, and the hydrogen gas is supplied to a fuel cell stack. The fuel cell stack generates electricity through an electrochemical reaction between the hydrogen gas and oxygen.
The fuel processor includes a desulfurizer and a hydrogen generator. The hydrogen generator includes a fuel reformer and a shift reactor. The desulfurizer removes sulfur from the fuel to prevent catalysts in the fuel reformer and the shift reactor from being adversely affected by sulfur compounds.
The fuel reformer produces hydrogen by reforming hydrocarbon, but also produces carbon dioxide and carbon monoxide. The carbon monoxide adversely affects a catalyst used for an electrode of the fuel cell stack. Therefore, the reformed fuel cannot be directly fed to the fuel cell stack, but must be passed through a shift reactor, which is a carbon monoxide removing apparatus. The shift reactor may reduce the carbon monoxide content in the fuel to less than 10 ppm.
To remove the carbon monoxide, the following three reactions, that is, shift reaction/ methanation reaction/PROX reaction have been used.CO+H2O→CO2+H2   [Reaction 1]CO+2H2→CH4+½O2   [Reaction 2]CO+½O2→CO2   [Reaction 3]
To obtain less than 10 ppm carbon monoxide content in the fuel using the above shift reaction, a shift reactor must be maintained at a temperature greater than 200° C. It takes about one hour to raise the temperature of the shift reactor to 200° C. However, it is a waste of time to wait for an hour to use electricity when electricity is readily available whenever it is necessary. Therefore, much research has been conducted to improve this adverse effect.
An apparatus using one burner that can sequentially heat a fuel reformer and a shift reactor has been disclosed in Japanese Patent Publication No. 2004-31280. When the shift reactor is heated using the burner for heating the fuel reformer, the shift reactor is separately positioned from the burner, and a long time is required to raise the shift reactor temperature to its operating temperature.
A system that heats the shift reactor using an additional electric heater has been disclosed in Japanese Publication Patent No. 2001-354404. However, this system consumes much electrical energy.
Accordingly, there is a need to develop a hydrogen generator that has a simple structure and can rapidly raise the temperature of a shift reactor.